1. Field of the Invention
The present invention relates to a magnetic recording and reproduction apparatus, and in particular to a magnetic recording and reproduction apparatus in which a sub chassis is movable relative to a main chassis.
2. Description of the Related Art
A magnetic recording and reproduction apparatus includes two chassis, i.e., a main chassis and a sub chassis, for recording information to, and/or reproducing information from, a magnetic tape accommodated in a cassette.
With reference to FIGS. 11, 12, 13, 14, 15, 16 and 17, a conventional magnetic recording and reproduction apparatus 600 will be described.
FIG. 11 shows a main chassis 400 of a conventional magnetic recording and reproduction apparatus 600. Part (a) of FIG. 11 is a left side view of the main chassis 400, and part (b) of FIG. 11 is a plan view thereof.
The following elements are provided on the main chassis 400: a rotatable head cylinder 402 for recording information to, and/or reproducing information from, a magnetic tape, a first projection guide section 404 projecting upward from the main chassis 400, and a second projection guide section 406 projecting upward from the main chassis 400.
In FIG. 11, the elements other than the rotatable head cylinder 402, the first projection guide section 404 and the second projection guide section 406 are omitted for the sake of simplicity.
FIG. 12 shows a sub chassis 500 of the conventional magnetic recording and reproduction apparatus 600. Part (a) of FIG. 12 is a left side view of the sub chassis 500, part (b) is a plan view thereof, and part (c) is a right side view thereof.
The following elements are provided on the sub chassis 500: a lock engaging section 502, a first guide groove 504, and a second guide groove 506. The lock engaging section 502 is provided at a right end of the sub chassis 500.
In FIG. 12, the elements other than the lock engaging section 502, the first guide groove 504, and the second guide groove 506 are omitted for the sake of simplicity.
FIG. 13 shows a cassette holder 550 of the conventional magnetic recording and reproduction apparatus 600. Part (a) of FIG. 13 is a left side view of the cassette holder 550, part (b) is a plan view thereof, part (c) is a right side view thereof, and part (d) is a front view thereof.
The cassette holder 550 includes an insertion opening 552 through which a cassette can be inserted, and a lock lever 554 for locking the cassette holder 550 to the sub chassis 500.
The lock lever 554 and the lock engaging section 502 shown in FIG. 12 are included in a locking section.
In FIGS. 11, 12 and 13, a mechanism for pulling out a tape from the cassette and winding the tape around the rotatable head cylinder 402, a mechanism for driving the tape and the like are omitted.
FIGS. 14 and 15 are each a schematic view of a cassette holder elevating section 560 of the conventional magnetic recording and reproduction apparatus 600. The cassette holder elevating section 560 moves the cassette holder 550 upward and downward with respect to the sub chassis 500. FIG. 14 shows a state where the cassette holder 550 has been moved up with respect to the sub chassis 500 by the cassette holder elevating section 560. FIG. 15 shows a state where the cassette holder 550 has been moved down with respect to the sub chassis 500 by the cassette holder elevating section 560.
The cassette holder elevating section 560 includes a first link 562, a second link 564, and a spring 566.
FIGS. 14 and 15 show a left side section 500a of the sub chassis 500 shown in FIG. 12. The side section 500a has a cam groove 500b therein. FIG. 12 shows only a bottom section of the sub chassis 500 and does not show the left side section 500a. 
A left side section of the cassette holder 550 has a cam groove 550a provided therein.
As shown in FIGS. 14 and 15, the first link 562 has a first end 562a and a second end 562b. The first end 562a is slidably engaged with the cam groove 500b, and the second end 562b is pivotably engaged with the left side section of the cassette holder 550.
The second link 564 has a first end 564a and a second end 564b. The first end 564a is slidably engaged with the cam groove 550a of the cassette holder 550, and the second end 564b is pivotably engaged with the left side section 500a of the sub chassis 500.
The first link 562 and the second link 564 are pivotably engaged with each other at an engaging point 564c. 
The spring. 566 is extended between the first link 562 and the second link 564. One end of the spring 566 is connected to the second end 562b of the first link 562, and the other end of the spring 566 is connected to the first end 564a of the second link 564. The spring 566 applies a force so as to reduce the distance between the second end 562b of the first link 562 and the first end 564a of the second link 564. This increases the distance between the sub chassis 500 and the cassette holder 550, and thus the cassette holder 550 moves upward with respect to the sub chassis 500.
In the above, the cassette holder elevating section 560 provided on a left side section of the magnetic recording and reproduction apparatus 600 is described with reference to FIGS. 14 and 15. On a right side section of the magnetic recording and reproduction apparatus 600, a mechanism similar to the cassette holder elevating section 560 is provided.
In general, a synchronization shaft is provided for synchronizing the first links provided on the left side section and the right side section and also synchronizing the second links provided on the left side section and the right side section. FIGS. 14 and 15 omit the synchronization shaft.
The cassette (not shown) is insertable at the state shown in FIG. 14 where the cassette holder 550 has been moved up. When the cassette holder 550 is pushed down from this state, the state shown in FIG. 15 is realized.
When the cassette holder 550 is pushed down onto the sub chassis 500, the lock lever 554 (FIG. 13) is engaged with the lock engaging section 502 (FIG. 12). This fixes the cassette holder 550 and the sub chassis 500 to each other to some extent. FIGS. 14 and 15 omit the lock lever 554 and the lock engaging section 502.
In general, the look lever 554 is pivotably provided to the cassette holder 550. A detailed mechanism for engaging the lock lever 554 with the lock engaging section 502 and releasing the lock lever 554 from the lock engaging section 502 is omitted from FIGS. 11 through 15. The lock section including the lock lever 554 and the lock engaging section 502 is provided only on the right side section of the magnetic recording and reproduction apparatus 600.
FIG. 16 shows the magnetic recording and reproduction apparatus 600 at a cassette mountable position. Part (a) of FIG. 16 is a left side view of the magnetic recording and reproduction apparatus 600, and part (b) is a plan view thereof.
FIG. 17 shows the magnetic recording and reproduction apparatus 600 at a tape pull-out position. Part (a) of FIG. 17 is a left side view of the magnetic recording and reproduction apparatus 600, and part (b) is a plan view thereof.
FIGS. 16 and 17 omit the cassette holder elevating sections, the mechanism for pulling out the tape from the cassette and winding the tape around the rotatable head cylinder 402, the mechanism for driving the tape and the like.
As shown in FIGS. 16 and 17, the first projection guide section 404 and the second projection guide section 406 provided on the main chassis 400 are respectively movably engaged with the first guide groove 504 and the second guide groove 506 provided in the sub chassis 500. Thus, the sub chassis 500 is reciprocally movably guided relative to the main chassis 400. In FIG. 16, the cassette holder 550 has been moved down with respect to the sub chassis 500. The sub chassis 500 is movable relative to the main chassis 400 from the cassette mountable position shown in FIG. 16 to the tape pull-out position shown in FIG. 17.
The magnetic recording and reproduction apparatus 600 has the following problems. The force at which the cassette holder 550 moves upward by the spring 566 is suppressed by the lock lever 554 and the lock engaging section 502. However, since the locking section including the lock lever 554 and the lock engaging section 502 is provided on the right side section of the magnetic recording and reproduction apparatus 600, the cassette holder 550 tries to move upward with respect to the sub chassis 500 and the main chassis 400 on the left side section of the magnetic recording and reproduction apparatus 600. As a result, the left side of the cassette holder 550 goes upward from the horizontal state of the cassette holder 550. Thus, the position of the cassette in the height direction is not determined with respect to the sub chassis 500 and the main chassis 400.
In order to solve this problem, it is conceivable to set the cassette 550 such that the left side of the cassette 550 is slightly lower than the right side thereof in the state where the cassette holder 550 has been moved up. This is made possible by offsetting the phase between the first link provided on the left side section and the first link provided on the right side section of the cassette holder elevating section and also offsetting the phase between the second link provided on the left side section and the second link provided on the right side section of the cassette holder elevating section. However, this causes another problem that the cassette holder 550 is tilted at the position where the cassette holder 550 has been moved up.
When the phase between the first links provided on the left side section and the right side section of the cassette holder elevating section and the phase between the second links provided on the left side section and the right side section of the cassette holder elevating section are offset as described above, the cassette holder 550 presses the sub chassis 500 downward in a state where the cassette holder 550 has been moved down by the variance in the phases. This force twists the sub chassis 500 and the main chassis 400. As a result, the tilt precision of the tape guide posts for guiding the tape in the recording and reproduction state of the magnetic recording and reproduction apparatus 600 is deteriorated, thus spoiling the stable running of the tape.